yes I'd make sure the master switch is grounded, disconnect the load, and check again - if it's 120V into the switch, and 60V out (measured AT the fixture), then the switch is bad or the wiring from switch to fixture is really bad.
uh yes I would expect a glow at an incandescent bulb but not an LED bulb.
I'm not an electrician - I'm a EE so I can prove my point with sketches and napkin calcs, and still trip the breaker.

That's really strange. I don't spin but when I cook chicken, usually cook at 250-300F then for last stage, I depend on indirect 350-400F for 30-60 minutes to crisp the skin. Otherwise it stays too rubbery.
The dome is not a good reference tho - you might have better luck referring to an actual grate temperature probe like Maverick ET-732 .
Maybe the fat just doesn't drain enough when you spin. But seems like it would just need more time.
I'd spike the chicken so it doesn't tumble, you don't want the rub to be rubbed off. Whats wrong with the forks.

2factor authentication (2FA) by SMS is better than nothing else, but it is not durable. FYI your phone number is not securely in your possession by default. There are many extreme examples of number-porting from high-value targets, that essentially steal your phone number to receive your 2FA texts It's been too easy to do, up to this point, and phone companies have been slow to recognize this threat to their customers. As long as you have a smartphone, tablet or PC then you can generate a durable second-factor (TOTP based) that cannot be easily ported away. I suggest Authy (android, iphone, Chrome extension and app) for this approach but there are several others. Google Authenticator is the standard, but it's barebones with no backup - it is more work when you get a new phone and you'd better have a good record.
The phone app/TOTP code generator on the phone, replaces the one-purpose hardware gadget you had. Very convenient.
There are techniques to prevent number porting orders, but phone companies can still screw it up.
As for the debit card, you can get one that is normally locked until you need to ring out, then unlock it with the smartphone, and relock every time. Some banks do it, some don't.
I agree credit cards are still hard to secure. An automatic one-time-use card# would be best - that is essentially what you get with Android Pay, or Apple Pay, or Samsung (whateverPay), but not many stores that I use, will do those.

in case of a failure (TTT sticking open, it will get thick and greasy), I'd like a slightly greater chance of limiting the runaway-grill/jet-engine effect, so that I might catch it before it consumes the grill and maybe the wooden deck. So I set the intake and exhaust dampers to the maximum amount I have ever needed for smoking, which is an inch or less open, on both. Then the TTT goes on the exhaust vent where it belongs. Then the likely-worst problem is that the grill burn might go out - and TTT will probably work to keep it going. That is the safest arrangement I can think of, for active temperature control. I am trying to not be the guy that had the smoker go nuclear and it burned down the house.
The TTT does not actually have to control 100% of the exhaust air to control the smoker temperature, and it can't anyway. There is always leakage in some amount, at the vent, at the lid seal. My guess is the TTT will still be able to maintain temperature control, if leakage is "low enough" that TTT has control of say 50% of the "total" exhaust flow including leakage, and the vents are throttled to reduce the max possible flow so that the grill/smoker temperature cannot runaway above 400, 500, 600F.
anyroad.

Brisket is just not as forgiving as pork shoulder. You can do "everything right" and still be punished by a bad piece.
Instead of taking the grate off, you might have rekindled it with a hair dryer, forcing air into the inlet vent, since you still had a coal. But if ash choked it in the first place then you could wind up losing the fire again, anyway.
I use and like the TTT also, bottom vent 1inch, top vent 0.5 - 0.75 inch at the edge, for smoking. Like shuley said maybe your vents are a little too closed. I wouldn't trust that iGrill anymore. The Maverick ET732 is used a lot - if it loses signal then it beeps and doesn't go quiet.
What I tend to do, is dig a hole to the fuel grate ("volcano", ha!) just to insure that air and exhaust has a free path. If the hole collapses during the burn, then the fire can go out. An expanded metal mesh tube might help ensure that the hole cannot be collapsed so easily in a long cook.
A hand torch make it easy to start as much or as little coals as you want.

you could leave it, or try to glue with epoxy or fireplace mastic. It'll probably crack some more, maybe it won't just fall apart.
Supposedly drilling a hole at the end of the crack, is a technique to stop it - I would not. The true end may not be perceptible.

I think I'm using the CG branded cover for the last 2-3 year - it kinda sucks. Thin, nylon strings tend to come out of the bottom hem. The vinyl coating tends to crack at the bottom hem. It might be ok for 4-5 years. I treated it with a waterproofing and UV-resistant wipe. Better than nothing, the grill must be covered to maximize its life, it's a rust collector.
I expect both types are the same construction.